Carrier-type heat-treatment apparatuses such as a mesh belt furnace described in Patent Literature 1 are known as apparatuses for heat-treating objects to be heat-treated. The mesh belt furnace includes a furnace main body including heaters, and a mesh belt that transports an object to be heat-treated thereinto. The mesh belt includes a mesh portion having a grid-net-like shape, the mesh portion being arranged on a surface of a conveyor portion formed of, for example, a steel band. This structure of the mesh belt enables an atmosphere in the furnace main body to be brought into contact with all peripheral surfaces of the object to be heat-treated. Furthermore, in Patent Literature 1, a mesh stage is arranged on the mesh belt to convect the atmosphere between the mesh belt and the mesh stage, thereby uniformly heat-treating the object to be heat-treated. Such carrier-type heat-treatment apparatuses are widely used because a large number of objects to be heat-treated can be heat-treated in one operation.